(a) Each instrument with static air case
connections must be vented to the outside atmosphere through an
appropriate piping system.

(b) Each static port must be designed
and located in such manner that the static pressure system performance is
least affected by airflow variation, or by moisture or other foreign
matter, and that the correlation between air pressure in the static
pressure system and true ambient atmospheric static pressure is not
changed when the airplane is exposed to the continuous and intermittent
maximum icing conditions defined in appendix C of this part.

(c) The design and installation of the
static pressure system must be such that --

(1) Positive drainage of moisture is
provided; chafing of the tubing and excessive distortion or restriction at
bends in the tubing is avoided; and the materials used are durable,
suitable for the purpose intended, and protected against corrosion; and

(2) It is airtight except for the port
into the atmosphere. A proof test must be conducted to demonstrate the
integrity of the static pressure system in the following manner:

(i) Unpressurized airplanes.
Evacuate the static pressure system to a pressure differential of
approximately 1 inch of mercury or to a reading on the altimeter, 1,000
feet above the airplane elevation at the time of the test. Without
additional pumping for a period of 1 minute, the loss of indicated
altitude must not exceed 100 feet on the altimeter.

(ii) Pressurized airplanes.
Evacuate the static pressure system until a pressure differential
equivalent to the maximum cabin pressure differential for which the
airplane is type certificated is achieved. Without additional pumping for
a period of 1 minute, the loss of indicated altitude must not exceed 2
percent of the equivalent altitude of the maximum cabin differential
pressure or 100 feet, whichever is greater.

(d) Each pressure altimeter must be
approved and must be calibrated to indicate pressure altitude in a
standard atmosphere, with a minimum practicable calibration error when the
corresponding static pressures are applied.

(e) Each system must be designed and
installed so that the error in indicated pressure altitude, at sea level,
with a standard atmosphere, excluding instrument calibration error, does
not result in an error of more than ±30 feet per 100 knots speed for the
appropriate configuration in the speed range between 1.23 VSR0
with flaps extended and 1.7 VSR1 with flaps
retracted. However, the error need not be less than ±30 feet.

(f) If an altimeter system is fitted
with a device that provides corrections to the altimeter indication, the
device must be designed and installed in such manner that it can be
bypassed when it malfunctions, unless an alternate altimeter system is
provided. Each correction device must be fitted with a means for
indicating the occurrence of reasonably probable malfunctions, including
power failure, to the flight crew. The indicating means must be effective
for any cockpit lighting condition likely to occur.

(g) Except as provided in paragraph (h)
of this section, if the static pressure system incorporates both a primary
and an alternate static pressure source, the means for selecting one or
the other source must be designed so that --

(1) When either source is selected, the
other is blocked off; and

(2) Both sources cannot be blocked off
simultaneously.

(h) For unpressurized airplanes,
paragraph (g)(1) of this section does not apply if it can be demonstrated
that the static pressure system calibration, when either static pressure
source is selected, is not changed by the other static pressure source
being open or blocked.